This invention relates to a power-assisted wheelchair and more particularly to an improved control arrangement therefor.
There have been provided a large number of different types of vehicles that are powered primarily by manual power, but wherein an electric motor assist is provided. The utilization of such electric motor assists permits the use of these types of vehicles by persons who might otherwise not be able to enjoy them. These vehicles can be utilized both for recreational and primary transportation purposes.
One type of vehicle wherein this form of power-assist system is particularly useful is in a wheelchair. By employing a power-assist for a wheelchair, it is possible to permit the user to obtain exercise and still travel substantial distances without assistance from another person.
Generally, one particularly useful way in which the power-assist is provided is that the amount of manual force input is sensed and an assist is provided in proportion to the manual power input. Although this has great utility, there are some areas where the prior art types of construction could be improved.
For example, many times the vehicle may be used by persons having varying strengths and abilities. In addition, at times, the same person may require different degrees of power-assist. For example if the terrain over which the vehicle changes more or less assist may be required. For example if going uphill, more assist may be required. On the other hand, when going down hill less assist is required. Often times these changes in condition may occur suddenly or even unexpectedly. Thus it is desirable to have the capability of having the assist be capable of responding rapidly to changes in conditions.
It is, therefore, a principal objection of this invention to provide an improved electric motor assisted vehicle wherein the system is more responsive to variations in manual input so as to set the appropriate degree of power-assist for the specific individual and specific circumstance.
One particularly sensitive area in connection with the power-assist provided is a potential danger of the vehicle being driven at too great a speed. Although it is possible to utilize speed limiting devices, the desired controlled speed also varies with many conditions. For example, on level ground or when going up a hill the need for speed control is not as great as when going down hill. In some instances it may even be desirable to have the assist system be capable of providing a braking effect.
It is, therefore, a still further object of this invention to provide an improved electric power-assisted vehicle operating system wherein the system will provide automatic braking under certain desired conditions.
However, at times when in a braking or speed controlling mode, conditions may require an abrupt change in assist amount.
It is, therefore, a still further object of this invention to provide an improved electric power-assisted vehicle operating system wherein the system can shift between braking and assist under certain conditions.
Another condition that is particularly important in dealing with power-assist is during changes in operating conditions, as above described. If the assist ratio is fixed so as to be substantially constant for a given individual or condition, then the assist ratio which may be acceptable for normal running may be too low to facilitate start-up or if the load conditions change. This is particularly true if it is necessary when going from the level to traveling up a hill.
It is, therefore, a still further object of this invention to provide an improved electric power-assisted vehicle control wherein the assist ratio is automatically adjusted so as to suit particular running conditions, such as going up hills.
Even when going up or down hills the desired amount of assist may change suddenly. For example if going down hill and the speed is being controlled by utilizing braking operation from the assist motor, the appearance of an unexpected article in the path may require sudden maneuvering. If the assist is being limited or even prevented this is undesirable.
It is, therefore, an object of this invention to provide an improved electric power-assisted vehicle control wherein the assist can be rapidly modified to suit changed conditions.
Generally, the manual torque input sensor for the control of this type of vehicle has a null or dead band range wherein the operator may cause some force application which is not sufficient to initiate operation of the vehicle. Although this type of dead band can be particularly useful in ensuring against the unexpected or sudden application of power-assist when it may not be desired, it can also delay assist operation once the vehicle is in motion.
It is, therefore, a still further object of this invention to provide an improved torque sensing arrangement for an electric power-assisted vehicle wherein the dead band condition can be adjusted, either manually or automatically, so as to provide different degrees of dead band, depending upon the running condition.
Certain of these results can be achieved by having the degree of power-assist vary in relation to the particular speed of travel of the vehicle. For example, it may be desirable to provide a high degree of power-assist when the vehicle speed is low or when first starting up, and then decrease the power-assist as the vehicle speed increases. However, if traveling under certain conditions, for example, when rolling downhill, the vehicle speed may increase, and if the power assist is decreased, then the amount of braking force available for the rider also would decrease.
It is, therefore, a still further object of this invention to provide an improved electric power-assisted vehicle control wherein the variations in the assist ratio can be tailored to provide the optimum degree of power assist under all running conditions.
Several features of this invention are adapted to be embodied in an electric motor, power assisted wheelchair having a frame assembly providing a seat for accommodating a single rider. A pair of drive wheels are disposed on opposite sides of the seat and have hand wheel portions so that the rider may apply a manual force for turning these drive wheels. In addition, an electric motor is provided that is capable of providing a driving assist force to at least one of the drive wheels for assisting the manual input. A sensor senses the manual force that the rider applies to the hand wheel. A control receives the output from the sensor and provides an amount of electric power assist from the electric motor in relation to the sensed manual input force.
In accordance with a first feature of the invention that is adapted to be embodied in a wheelchair as described above, the vehicle running condition is also sensed, and the amount of power assist provided is varied with each input of manual force and in response to the sensed vehicle running condition.
In accordance with a specific embodiment incorporating the aforenoted feature, a specific amount of assist is provided when the vehicle speed is below a predetermined speed, and the assist decreases when the speed exceeds this predetermined speed.
In accordance with another specific embodiment incorporating the aforenoted feature, a braking effect may be generated when a predetermined speed is exceeded.
In accordance with another specific embodiment incorporating the aforenoted feature, a greater amount of assist is provided when the speed falls below a predetermined speed.
In accordance with another specific embodiment incorporating the aforenoted features, the predetermined speeds are reset with each new application of manual force.
In accordance with still another specific embodiment incorporating the aforenoted features the assist is maintained for a time period after the application of manual input ceases.
Other features of the invention are adapted to be embodied in an electric power assisted, manually propelled vehicle. The vehicle has a propulsion device for propelling the vehicle. A manual input mechanism is provided for applying manual power to the propulsion device for manually powering the vehicle. An electric motor is operatively coupled to the vehicle propulsion device for applying an assist power to the propulsion device. A control senses the manual input force and other conditions for controlling the amount of power-assist provided.
In accordance with a first feature of the invention in connection with an electric power assisted vehicle as described above, if the vehicle speed exceeds a predetermined speed, the power assist is stopped. If the speed exceeds a second predetermined speed higher than the first predetermined speed, a braking force is applied to the vehicle through the electric motor by means of regenerative braking.
In accordance with yet another embodiment of the invention as described in the described type of electric power assisted vehicle, a manual input sensor of the control has a null or dead band condition wherein a predetermined amount of force must be exerted before the electric power-assist is applied. In accordance with this feature of the invention, the null or dead band range is set wider before the vehicle is in motion than during running, so as to decrease the sensitivity. However, once the vehicle is in operation, the width of the null or dead band is decreased, so as to provide quicker response.